This invention relates to apparatus for warming fluids for medical applications, and more particularly to apparatus for immersion in a fluid to be warmed that is selectively powered and sensed to assure fail-safe operation in and out of the fluid to be warmed.
Many medical procedures require warming fluids in a sterile environment at elevated temperatures that are closely regulated within a narrow range of temperatures. In addition, inexpensive, pre-sterilized, disposable equipment greatly facilitates preparation and clean-up procedures associates with a surgical procedure, and promotes the preservation of sterile conditions from patient to patient.
Electrically-controlled heaters for warming liquids or gases associated with surgical procedures have attained wide acceptance but commonly must be sterilized prior to re-use. Disposable heater units obviate the need for re-sterilization between uses, but inexpensive, single-application heaters to date have not included sufficiently high quality workmanship, materials and designs to assure reliable operation throughout an entire surgical operation. For example, safety features such as thermal cutoff switches typically do not operate satisfactorily if only a portion of an immersed heater remains in contact with a liquid to be warmed. Also, mass production techniques commonly associated with inexpensive, disposable heaters typically are incapable of maintaining close tolerances of electrical parameters to assure repeatable performance from a population of heaters operated in a given surgical application. Such variations in electrical parameters usually contribute to difficulties in controlling the operating temperature within close tolerances.